Fixed source culture for DeepL service

I18N Commander/Processor/DeepL.cs

@@ -52,6 +52,9 @@ public static class DeepL
             var sourceCultureIndex = await AppSettings.GetDeepLSourceCultureIndex();
             var sourceCulture = await AppSettings.GetCultureCode(sourceCultureIndex);
             
+            // In case of the source culture, we cannot specify the region, so we need to remove it:
+            sourceCulture = sourceCulture.Split('-')[0];
+            
             using var deepl = new Translator(deepLAPIKey);
             var translation = await deepl.TranslateTextAsync(text, sourceCulture, targetCulture);